1. Field of the Invention
The present invention relates to a field emitter device, and more particularly, to a field emitter device comprising carbon nanotubes.
2. Description of the Related Art
A field emitter device is used as a field emitter source for a field emission display (FED) as one of the promising next generation flat displays. The field emitter device provides high picture quality, high efficiency, and low power consumption, compared to conventional cathode ray tubes.
The performance of the field emitter device relies on processing techniques applied to fabricate the same and its stability. Recently, many attempts have been made to apply a highly conductive, stable carbon nanotube to the field emitter device.
In the field of displays, a field emitter device including carbon nanotubes is manufactured typically by a plasma chemical vapor deposition method disclosed in U.S. Pat. No. 6,232,706 and a method using a paste disclosed in U.S. Pat. No. 6,239,547.
According to the plasma chemical vapor deposition method, ethylene gas is injected between two electrodes in a reactor in the presence of a nickel catalyst, and the ethylene gas is energized by a direct current or high-frequency electric field to generate plasma by glow discharge and thus to grow carbon nanotubes on the electrode using the plasma energy.
According to the field emitter device fabricating method using the paste, carbon nanotubes are processed into carbon nanoparticles by laser ablation or arc discharge, mixed with a conductive or non-conductive paste, and printed.
In the conventional plasma chemical vapor deposition method, due to a high voltage applied between the field emitter tip and an anode, the remaining plasma gas occurs arcing to damage the carbon nanotubes. Here, “arcing” refers to a an instantaneous electrical short between the anode and a gate electrode in a vacuum tube where the field emitter device is placed, which increases a voltage applied to the gate electrode and thus damages a gate insulating layer and a resistive layer.
In the conventional field emitter device fabricating method using the paste, the carbon nanoparticles are mixed with a costly silver paste or polymeric compound and thermally treated at a temperature of 350-500° C. As a result, the carbon nanoparticles are oxidized to reduce the lifetime of the carbon nanoparticles. In addition, in the manufacture of a field emitter device fabricating apparatus using this method, an extended period of heating time is required, and outgassing induces gas, such as oxygen, to remain and to be adsorbed onto the carbon nanoparticles, thereby suppressing electron emission and reducing the lifetime of the field emitter device.
FIG. 1 is a transmission electron microscopic (TEM) photograph of conventional carbon nanotubes. Field emission characteristics of the conventional carbon nanotubes shown in FIG. 1 with respect to time are shown in FIGS. 2A and 2B.
Referring to FIG. 1, the field emission characteristics were measured in a vacuum of 1×10−7 mbar from starting up to 8 hours, in an oxygen atmosphere of 1×10−6 mbar up to 11 hours and an increased oxygen pressure of 5×10−5 mbar up to 17 hours, and in a vacuum of 1×10−7 mbar. When the oxygen pressure was increased to 5×10−5 mbar after passing 11 hours from the start, a great degradation in the field emission characteristics is apparent. When the measuring condition was back to the vacuum, the current emission was instantaneously increased but reduced in a short period of time. The current emission drop following the instantaneous increase after passing 21 hours from the start is because the remaining carbon nanotubes undamaged by oxygen suddenly emit electrons and disappear as the measuring condition is changed to the vacuum where impurities such as oxygen do not exist.
Referring to FIG. 2B, as oxygen injection is started after a vacuum of 2×10−7 mbar is maintained for 3 hours and 40 minutes, the current emission drops from 1 μA to 10−6 μA. When the condition was changed back to the vacuum after 6 hours and 40 minutes were passed from the start, the field emission characteristic was not recovered to that in the initial vacuum condition.
In other words, when a remaining gas, such as oxygen, exist in the conventional field emitter device, current emission greatly decreases over time and is not recovered to an initial level of the current emission even when the oxygen is evacuated to create the initial vacuum condition.